The present invention relates to substantially transparent flame retardant halogen-free aromatic polycarbonate compositions More particularly, the present invention relates to the use of certain triarylsilanes, such as triphenylvinylsilane or triphenylsilanol to impart UL-94 V-O flame retardant properties to aromatic polycarbonates without adversely affecting their transparency.
Aromatic polycarbonate, such 2,2-bis-(4-hydroxyphenyl)-propane or bisphenol A polycarbonates have found wide use in glazing applications. However, it is widely known that BPA polycarbonate often cannot be blended with other materials without adversely affecting its transparency.
In copending application Ser. No. 07/319,026, filed Mar. 6, 1989, for flame retardant aromatic polycarbonate blends, improved flame retardant properties can be achieved with polycarbonates by incorporating into the polycarbonate certain arylenesilicon materials, such as silicone polyimides or aromatic polyester-siloxane block copolymers. Additional organosilicon materials are employed as plasticizers with polycarbonates as shown by Mark et al., U.S. Pat. No. 4,230,661, while Acquiri et al., U.S. Pat. No. 4,273,691 and Frye, U.S. Pat. No. 4,387,176 teach that certain silicone materials or silicone blends, when used in combination with alkaline earth metal salts, can impart improved flame retardant properties to various organic polymers. Experience has shown, however, that although improved flame resistance has been imparted to aromatic polycarbonates utilizing the aforementioned flame retardants, undesirable toxic by-products of combustion often are emitted which have interfered with the commercial acceptance of flame retardant polycarbonates in many instances. In addition, although in some instances flame retardants have been used in polycarbonates which have not resulted in undesirable toxic by-products during burning as taught in copending application Ser. No. 319,026, it has been difficult to achieve UL-94 V-O flame retardance if the flame retardant blend is tested at a thickness of less than 1/8", such as 1/16".
It would be desirable therefore to provide aromatic polycarbonate compositions which are transparent and which can provide UL-94 V-O flame retardancy. As used hereinafter, the term flame retardant means that the flame retardant polycarbonates have satisfied UL94 V-O requirements for flammability, as shown by the "Flammability of Plastic Materials Bulletin" of Jan. 24, 1980. More particularly, a 5".times.1/2".times.1/16" polycarbonate test bar containing an effective amount, as defined hereinafter, of the flame retardant, is suspended vertically over a 3/4" Bunsen Burner flame as provided in the aforementioned UL94 test. The test sample preferably exhibits a UL94 V-O rating which includes the following criteria:
A. Not have any specimen which burn with flaming combustion for more than 10 seconds after application of the test flame. PA1 B. Not have a total flaming combustion time exceeding 50 seconds for 10 flame applications for each set of five specimens. PA1 C. Not have any specimens which burn with flaming or glowing combustion up to the holding clamp. PA1 D. Not have any specimens which drip flaming particles that ignite dry absorbent surgical cotton located 12 inches (305 mm) below the test specimen. PA1 E. Not have any specimens with glowing combustion which persists for more than 30 seconds after the second removal of the test flame.